DESCRIPTION

getgroups() returns the supplementary group IDs of the calling process
in list. The argument size should be set to the maximum number of
items that can be stored in the buffer pointed to by list. If the
calling process is a member of more than size supplementary groups,
then an error results. It is unspecified whether the effective group
ID of the calling process is included in the returned list. (Thus, an
application should also call getegid(2) and add or remove the resulting
value.)
If size is zero, list is not modified, but the total number of
supplementary group IDs for the process is returned. This allows the
caller to determine the size of a dynamically allocated list to be used
in a further call to getgroups().
setgroups() sets the supplementary group IDs for the calling process.
Appropriate privileges (Linux: the CAP_SETGID capability) are required.
The size argument specifies the number of supplementary group IDs in
the buffer pointed to by list.

RETURNVALUE

On success, getgroups() returns the number of supplementary group IDs.
On error, -1 is returned, and errno is set appropriately.
On success, setgroups() returns 0. On error, -1 is returned, and errno
is set appropriately.

ERRORS

EFAULTlist has an invalid address.
getgroups() can additionally fail with the following error:
EINVALsize is less than the number of supplementary group IDs, but is
not zero.
setgroups() can additionally fail with the following errors:
EINVALsize is greater than NGROUPS_MAX (32 before Linux 2.6.4; 65536
since Linux 2.6.4).
ENOMEM Out of memory.
EPERM The calling process has insufficient privilege.

CONFORMINGTO

SVr4, 4.3BSD. The getgroups() function is in POSIX.1-2001. Since
setgroups() requires privilege, it is not covered by POSIX.1-2001.

NOTES

A process can have up to NGROUPS_MAX supplementary group IDs in
addition to the effective group ID. The set of supplementary group IDs
is inherited from the parent process, and preserved across an
execve(2).
The maximum number of supplementary group IDs can be found using
sysconf(3):
long ngroups_max;
ngroups_max = sysconf(_SC_NGROUPS_MAX);
The maximum return value of getgroups() cannot be larger than one more
than this value.
The original Linux getgroups() system call supported only 16-bit group
IDs. Subsequently, Linux 2.4 added getgroups32(), supporting 32-bit
IDs. The glibc getgroups() wrapper function transparently deals with
the variation across kernel versions.